J Musculoskelet Neuronal Interact 2013; 13(4):395-404
Original Article
Hylonome
Gymnastics participation is associated with skeletal benefits in the distal forearm: a 6-month study using peripheral Quantitative Computed Tomography L.A. Burt1, G. Ducher1, G.A. Naughton1, D. Courteix1,2, D.A. Greene1 1
Centre of Physical Activity Across the Lifespan, Australian Catholic University, Locked Bag 2002, Strathfield, NSW, Australia, 2135; 2Clermont Université, Université Blaise Pascal, EA 3533, Laboratoire des Adaptations Métaboliques à l’Exercice en Conditions Physiologiques et Pathologiques, Clermont-Ferrand, France
Abstract Objectives: Musculoskeletal development of the upper limbs during exposure to weight-bearing loading is under-researched during early pubescent growth. The purpose was to assess the changes in upper body musculoskeletal strength in young girls following 6 months of non-elite gymnastics participation. Methods: Eighty-four girls, 6-12 years were divided into groups based on gymnastics participation: high-training (HGYM, 6-16 hr/wk), low-training (LGYM, 1-5 hr/wk), and non-gymnasts (NONGYM). Volumetric BMD, bone geometry, estimated bone strength and muscle size were assessed at the non-dominant forearm (4% and 66% radius and ulna) with pQCT. DXA assessed aBMD and body composition. Tests for explosive power, muscle strength, and endurance were also performed. Results: Interaction effects were observed in all variables at the 4% radius. At the 66% ulna, HGYM and LGYM had greater bone mass, size and bone strength than NONGYM, furthermore a dose-response relationship was observed at this location. Body composition was better for HGYM than LGYM and NONGYM, however muscle function was better for HGYM and LGYM than NONGYM. Conclusion: The greatest changes were obtained with more than one gymnastics class per week. Separating gymnastics participation-related changes from those associated with normal growth and development remains difficult, particularly at the 4% radius. Keywords: Artistic Gymnastics, Upper Limb, Longitudinal, Musculoskeletal, Female
Introduction Participation in elite gymnastics may be related to positive musculoskeletal health outcomes1,2 however, the injury risk3,4 associated with the training volume and intensity (>25 hr/wk)5 make it unsuitable for the promotion of physical activity within the general population. Non-elite gymnastics participation involves fewer training commitments, psychological demands, nutritional and hormonal disturbances, and a reduced preva-
The authors have no conflict of interest. Corresponding author: Lauren A. Burt, Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Dr, NW, Calgary, Alberta, Canada, T2N 1N4 E-mail:
[email protected] Edited by: F. Rauch Accepted 17 July 2013
lence of injuries compared with participation in elite gymnastics4,6,7. As a consequence, an increasing number of studies are investigating the association of non-elite gymnastics participation on skeletal properties8-12. Musculoskeletal relationships associated with non-elite gymnastics participation are expected to be smaller than relationships associated with elite gymnastics and may vary based on exposure to the sport. To detect these relationships, it is necessary to account for growth, maturation and other potential confounders in longitudinal investigations. Previous longitudinal studies on non-elite gymnasts used dual-energy X-ray absorptiometry (DXA)11,13-15, a 2D imaging modality which cannot measure 3D bone density or geometry. In contrast, peripheral quantitative computed tomography (pQCT) is able to assess 3D total bone and compartmental properties. Despite slightly higher variability in pQCT than DXA, pQCT has previously been used in several cross-sectional studies in pre- and early pubertal gymnasts10,16,17 and one longitudinal study on male and female pre-pubertal gymnasts18. 395
L.A. Burt et al.: Non-elite gymnasts: musculoskeletal strength
The notion of the muscle-bone relationship is not new however, most studies use surrogate measures of muscle force and function such as lean mass when analysing the muscle-bone relationship19-21. Few studies have assessed actual muscle function in addition to bone health among young gymnasts12,14,22. One study reported changes in muscle function over time; reporting gymnasts had greater muscle strength than non-gymnasts at baseline however, no difference between groups was evident at follow-up14. The minimum amount of training necessary to induce positive musculoskeletal changes in young gymnasts is currently unknown. Reviews of exercise interventions in children and adolescents show two to three sessions per week are typically prescribed for improving musculoskeletal health23,24. However, gymnastics is associated with high-intensity loading, and a unique bilateral loading pattern of the upper and lower limbs, as opposed to the majority of sports that only load the lower limbs. Whether or not the same overall exposure, resulting from a single session of gymnastics per week (i.e. 2-3 hours) provides sufficient improvements in short-term musculoskeletal health benefits is unclear. The aim of the study was to compare the changes in musculoskeletal parameters over six months in early pubertal female artistic gymnasts participating in different training volumes (high-10.5 hr/wk and low-3 hr/wk) with a group of age- and gender-matched non-gymnasts. Specifically, gymnasts were expected to have greater increases in upper limb muscle function and skeletal parameters than non-gymnasts. Furthermore, we hypothesized a dose-response relationship would emerge between gymnastics exposure and the increases in musculoskeletal parameters.
Methods Study participants Prior to participant recruitment, the study was approved by the University’s ethics committee. Initially, 141 early pubertal girls were invited to participate in this longitudinal study. After obtaining informed parental consent and child assent, a total of 94 participants completed baseline assessments, three of whom were excluded as they did not meet the early pubertal selection criterion (≤ Tanner Stage II). Following six months of growth and development, 91 girls completed subsequent assessment. Seven girls dropped out at follow up as they were unable to attend scheduled appointments. There were no baseline-related bone differences between girls who dropped out of the study and those who completed the study. Therefore, 84 young girls were included in this study. Participants were assigned to one of three groups based on their gymnastics participation: high-training gymnasts (HGYM; n=28), 6 to 16 hr/wk, low-training gymnasts (LGYM; n=28), 1 to 5 hr/wk and non-gymnasts (NONGYM; n=28). The cut-off point of 5 hr/wk, used to discriminate HGYM and LGYM, was chosen based on the number of training sessions per week: LGYM participated in one gymnastics class per week 396
(never exceeding 5 hr/wk), whereas HGYM participated in more than one class per week (always exceeding 5 hr/wk). HGYM participants involved in the study were training 16 hr/wk or less, which is significant however, this involvement is still considered a non-elite level, and is associated with normal growth and maturation25. At study initiation, participants were healthy early pubertal girls, not taking any medication known to affect bone or muscle metabolism, and without a fracture to the upper limb within the previous 12 months. Gymnasts were recruited from local gymnastics centres and were training between 1 and 16 hr/wk. Gymnasts had trained for at least six months in the sport and were participating at a recreational or non-elite level. Non-gymnasts were involved in less than 4 hr/wk of organised physical activity outside school and were recruited via the “bring a friend” recruitment strategy.
Setting Recruitment took place over a nine-month period. The total duration of the study was 15 months. All assessments were conducted in the University’s laboratory. The average time between baseline and follow up assessments was six months (range 5 to 8 months, mean 6.1, SD 0.82).
Power analysis To allow for the detection of significant differences in skeletal characteristics with a small estimated effect size (d=0.20), with a statistical power of 90% and a significance level of 0.05, the minimum total sample size was calculated to be 84 participants26.
Anthropometric assessment A stadiometer (SECA height rod model 220, Hamburg, Germany) with an accuracy of 0.1 cm was used to measure standing and sitting height. Body mass was recorded using digital scales (A&D Company Ltd., Tokyo, Japan) with an accuracy of 0.05 kg.
Body composition and areal Bone Mineral Density Whole body areal bone mineral density (aBMD), bone mineral content (BMC), bone area, lean and fat mass were measured by dual-energy X-ray absorptiometry (DXA, Norland, XR-36 System, Fort Atkinson, Wisconsin). Body composition and bone parameters in the upper limb (including the humerus, ulna, radius, carpals, metacarpals and phalanges) were derived from the whole body scan. Measurements were performed at the predetermined scan mode (speed 180 mm/s, resolution 6.5 x 13.0 mm, source collimation 1.68 mm) with the analysis software provided by the manufacturer (2.5.3a). The same technologist conducted and analysed all DXA scans. The CV in our laboratory was obtained following scanning of nine healthy university students twice, following repositioning. Specifically, CV’s were
